Ever wondered how much your pet’s diet impacts the environment?

There are approximately 163 million dogs and cats kept as pets in the US, and it’s safe to assume even most vegetarians feed their pets some kind of non-vegetarian food product, given that dogs and cats are both carnivorous species.

That got University of California, Los Angeles (UCLA) geography professor Gregory Okin wondering: Just how bad is the production of pet food for the environment?

Meat production has well-documented impacts on the environment, as Okin notes in a study he published this month in the journal PloS ONE: “Compared to a plant-based diet, a meat-based diet requires more energy, land, and water and has greater environmental consequences in terms of erosion, pesticides, and waste.”

Based on a poll conducted last year by the Baltimore, Maryland-based Vegetarian Resource Group, an estimated eight million adults in the United States identify as vegetarian. That’s 3.3 percent of the adult population in the US who abstain from eating any meat, seafood, or poultry (that number includes adults who identify as vegan, meaning they do not eat eggs or dairy, either).

Many people who have chosen to become vegetarian cite the harmful impacts of meat production on the environment as one of their reasons for doing so. Meanwhile, there are approximately 163 million dogs and cats kept as pets in the US, and it’s safe to assume even most vegetarians feed their pets some kind of non-vegetarian food product, given that dogs and cats are both carnivorous species. That got University of California, Los Angeles (UCLA) geography professor Gregory Okin wondering: Just how bad is the production of pet food for the environment?

As a professor of geography and member of the Institute of the Environment and Sustainability at UCLA, Okin’s research is usually focused on things like desert landscape dynamics and how they impact local ecosystems and the global climate. He first became interested in looking at the environmental impacts of pet food while considering the growing number of Americans raising chickens in their backyards.

“I was thinking about how cool it is that chickens are vegetarian and make protein for us to eat, whereas many other pets eat a lot of protein from meat,” he said in a statement. “And that got me thinking — how much meat do our pets eat?”

Meat production has well-documented impacts on the environment, as Okin notes in a study he published this month in the journal PloS ONE: “Compared to a plant-based diet, a meat-based diet requires more energy, land, and water and has greater environmental consequences in terms of erosion, pesticides, and waste.”

He adds that, with an estimated 77.8 million dogs and 85.6 million cats as of 2015, the US has the most pet cats and dogs of any country on Earth — and the meat-based diets of those pets have considerable consequences. “In addition to requiring greater land compared to plant crops to produce equivalent protein energy, and contributing to soil erosion, animal production has considerably greater impacts on water use, fossil fuel use, greenhouse gas emission, fertilizer use, and pesticide use. Despite the fact that more than 60% of US households have pets, these consumers of agricultural products are rarely included in calculations of the environmental impact of dietary choices.”

Using publicly available information from sources like the American Pet Products Association, the American Kennel Club, and the US Department of Agriculture, Okin was able to calculate that Americans’ dogs and cats consume about as many calories as the entire population of France every year, or about 19 percent as many calories as Americans themselves. But because dog and cat food typically contains more meat than the average human diet, our canine and feline companions actually consume about 25 percent of the total calories derived from animals in the US.

In fact, according to Okin, if the 163 million cats and dogs in the US were to somehow found their own country, that country would rank fifth in global meat consumption, behind only Brazil, China, Russia, and the US.

As a result, Americans’ pet cats and dogs produce about 30 percent as much feces, by mass, as the humans in the US, and their diet is responsible for 25 to 30 percent of the environmental impacts of producing food derived from animals. Dog and cat food is also responsible for the release of so much methane and nitrous oxide, both potent greenhouse gases, that it’s equivalent to driving 13.6 million cars for a year or releasing 64 million tons of CO2 into the atmosphere.

Okin writes in PloS ONE that the point of his study was not to argue for decreased pet ownership, as our furry friends “provide a host of real and perceived benefits to people including companionship, increased physical activity, improved mental health and social capital, benefits for child development, and social status.” Many dogs are also service animals, as well, while cats have long provided services such as pest control to humans, and Okin does not discount these positive impacts of pet ownership, either.

Rather, he wants people to be aware of the fact that dog and cat ownership is not “an unalloyed good,” and suggests that vegetarian pets like hamsters and birds might confer some of the same benefits as cats and dogs while having a much smaller impact on the environment.

It’s not just what Americans feed their pets that needs to be addressed, however. How much American feed their pets is another issue, as it makes the animals overweight and unhealthy while also making a major contribution to the unsustainability of pet food production. The pet food industry is already aware of these issues, he notes, and is working to reduce overfeeding and waste while looking for alternative sources of protein.

“I like dogs and cats, and I’m definitely not recommending that people get rid of their pets or put them on a vegetarian diet, which would be unhealthy,” Okin said. “But I do think we should consider all the impacts that pets have so we can have an honest conversation about them. Pets have many benefits, but also a huge environmental impact.”